Syrian president Bashar al Assad has vowed to crush foreign plots and fight
"terrorism" as his forces pounded rebel-held towns and blasted a bridge used
by refugees to escape to Lebanon.

"The Syrian people, who have in the past managed to crush foreign plots ... have again proven their capacity to defend the nation and to build a new Syria through their determination to pursue reforms along with the fight against foreign-backed terrorism," Assad said, quoted by state news agency SANA.

Assad, speaking during a meeting with a delegation from the Ukrainian parliament, said his country was clearly being targeted by outside forces seeking to undermine his regime.

"Any country draws its strength from the backing of its people," he said.

The 46-year-old president has consistently blamed the one-year revolt threatening his regime on foreign-backed "terrorist gangs".

The violence comes amid a flurry of diplomatic initiatives launched separately by the Arab League, the United Nations, Russia and China - all aimed at ending the year-long tumult in Syria which the UN says has killed at least 7,500 people.

Soldiers in tanks and armoured carriers stormed the town of Herak in the province of Daraa, while army deserters clashed with troops overnight in villages of Deir Ezzor, eastern Syria, the Syrian Observatory for Human Rights said.

The Britain-based watchdog also reported that troops backed by tanks circled the town of Tibet al-Imam in the central province of Hama and sent artillery shells crashing into Maaret al-Numan city in northwestern Idlib province.

The head of the Observatory, Rami Abdel Rahman, told AFP in Beirut that Syrian forces Tuesday also bombed a bridge used to evacuate the wounded and refugees to Lebanon from the central flashpoint province of Homs.

The bridge was in the village of Rableh, some three kilometers (nearly two miles) from the Lebanese border, and straddles the Orontes River.

Hadi Abdallah, a Syrian activist in Homs, said the bridge was used last week to transport wounded French reporter Edith Bouvier out of Homs, which has been the target of a fierce assault by regime forces.

"The bridge was hit by artillery shells," said Abdallah, reached by telephone from Beirut. "It can no longer be used."

The International Committee of the Red Cross, meanwhile, negotiated for a fourth day Tuesday with Syrian authorities to be allowed to deliver aid and evacuate the wounded from the battered Baba Amr rebel district of the city of Homs.

Dana Sleiman, of the United Nations refugee agency, said 170 families had sought refuge in the border Lebanese village of El Fakha, located in the eastern Bekaa region, and 50 others were in the nearby town of Aarsal.

"We are trying to verify whether there are additional people in other areas and how many have returned to Syria," Ms Sleiman said.

She said the UNHCR, in cooperation with local non-governmental organisations, was sending food, blankets and other aid to the refugees.

Ms Sleiman said each family accounted for six or seven members.

Ahmad Moussa, a spokesman for the Committee of Syrian Refugees in Lebanon, said some 65 families had arrived in northern Lebanon on Monday, some of them having moved on from the Bekaa region.

He said the majority were from the town of Homs, which has been the focus of a fierce assault by Syrian regime forces, and nearby Qusayr.

There have been conflicting reports on the number of refugees crossing into Lebanon in recent days. Officials on Monday said most of some 2,000 Syrians who had fled the violence in Homs province at the weekend had returned home after the fighting eased.

According to the UN High Commissioner for Refugees, 7,058 Syrians have registered in Lebanon as refugees but that number is expected to rise with the new influx of arrivals.

On Monday, Syrian forces bombarded the city of Rastan, a rebel bastion in neighbouring Homs province for a second day running, monitors said.

Rastan, which activists expect to be the next target of a drive by regime forces to expel rebels who have regrouped from Homs, 20 kilometres (12 miles) away, came under renewed shelling, the Observatory said.

"What's happening in Rastan is exactly what happened in Baba Amr: a siege, artillery fire and rockets," said Hadi Abdullah, an activist in Homs of the Syrian Revolution General Commission.

"Free Syrian Army fighters are still in Rastan. They will not give up because nobody wants another Baba Amr," he said.

With diplomatic efforts so far stymied, US Senator John McCain, an influential Republican, called for American air strikes on Syrian forces to protect population centres and create safe havens.

"Time is running out," Mr McCain - a hawk on both Syria and Iran - said in remarks on the floor of the Senate.

At the request of the Syrian opposition, Mr McCain said, "the United States should lead an international effort to protect key population centres in Syria, especially in the north, through air strikes on Assad's forces."

It also emerged that new efforts by the UN to condemn Assad are set to be blocked by Russia for the third time.

Russia believes that a new UN Security Council resolution on Syria reportedly being drafted by the United States is not balanced, the country's deputy foreign minister said.

The "new US draft of the UNSC resolution on Syria is a slightly modified version of the last vetoed document. It should be substantially balanced," Deputy Foreign Minister Gennady Gatilov wrote on his Twitter account late Monday.

Former UN chief Kofi Annan is on Wednesday to launch a mission aimed at convincing Assad to silence the guns blamed for thousands of deaths since anti-regime protests broke out last March.

Mr Annan is to hold talks with Arab leaders in Cairo before he heads to the Syrian capital on Saturday as joint special envoy for the United Nations and the 22-member Arab League.

The seasoned negotiator himself called it "a tough challenge" last week when he was named to the post.

UN humanitarian chief Valerie Amos said Damascus has finally approved a visit, to take place from Wednesday to Friday.

The aim of her visit would be "to urge all parties to allow unhindered access for humanitarian relief workers so that they can evacuate the wounded and deliver essential supplies," she said.